Hello Dan and Welcome to D.J Chat
Firstly, I reckon that your business plan is around 90% accurate!, however we just need to work on the last 10% which is mainly equipment selection.
Okay, the area's that we need to look at, firstly Tom is correct - you have been advised well over the top for your sound system

where as your lightshow will be a little bit lost when you come to do larger venues. If you plan on buying a 1000w sound system then you'll find that you budget is around £700 lighter after just buying your Amp & Speakers - which doesn't leave a lot for other items!.
Most people start out with either a 500W Sound System or a 800W Sound System and these are enough for most village halls and Childrens Disco's - (I remember the first kids disco that I did and most of the younger infants ran around with their hands over their ears!). Even for a High School Disco - you'll find that an 800W amp will see you through.
Okay lets look at the Larger Sound System First:-
Soundlab Sp800 - 2x 400W amp @ £249.00
Pair of Idex 15" Loudspeakers @ £269.00
Twin CD Player @ £199.00
4 Channel Mixer - £99.00
Flightcase - £60.00
Okay now the Smaller system:-
Soundlab SP500 Amplifier 2x 250W @ £150.00
Pair of Soundlab 15" Loudspeakers @ £129.00
Twin Cd Player @ £199.00
4 Channel mixer @ £99.00
Flightcase £60.00
We would throw in a basic mic, headphones and all leads free of charge.
Lighting - well avoid the strobe for a start since most schools ban them (because young kids are more subseptable to fits - and the School - and YOU don't want that sort of problem) and most adults hate them as well! so your budget would be better spent elsewhere.
Some sort of Moonflower effect makes a good centrepiece - We can offer a pair of DMX 250W Vista's for only £189 which link together and look very effective.
Here is my suggestion for a lightshow:-
Pair of DMX Vista's or similar at £189.00
Soundlab Blaze 250W moonflower @ £60.00
Tripod Lighting Stand @ £32.00
Soundlab Remote Fog Machine @ £45.00
I use a fogger which has a timer facility and never use the timer!. Since they cost around twice the price of a similar non timer machine it is a waste of money!. Basically it's not much effort to push a button for a few seconds now and again - even my "Roadies" manage to do that
Okay based on the smaller system we have:-
£637.00 for Audio
£326 for quite an impressive lightshow
Making a total of £963 - even allowing an extra £30 for delivery you are still well within your budget!.
If you choose the larger system you would be £32 OVER budget at a total of £1232 however, this isn't bad for a 800W system with intelligent lighting.
I would advise against buying anything with GENI on it

- I seem to spend half of my life repairing their lighting (Look in the "tech" area of our forum for one customers' story!). If you do want to swap the Vista Moonflowers for a Scanner then we can offer the Soundlab Cyclops for around the same price as the VISTAS for a PAIR!.
Okay, insurance - it is a legal requirement to have public liability insurance. this means that for a yearly fee you are insured aganst any damage to persons attending your disco through negligence on your part. This means that if somebody electrocutes themselves by touching a live piece of equipment, or a speaker falls of the stage onto them, then you are covered by your policy if they decide to take you to court and sue you for damages. Most policies will cover you for between £1million and £3million worth of liability which is usually enough even in the event of somebody being badly injured or - god forbid - a fatality.
Insurance isn't that expensive but you do need to arrange it. We have "Mikeee" from the TVDJA organisation who sometimes visit's this forum. I know that they offer reasonable rates of public liability through a yearly subscription to their organisation. I don't know whether they would accept you since you are only 15 - perhaps Mikeee could comment on any age restrictions?. If you want to find out more about the TVDJA their link is in our "DJ links section".
Advertising - well you do need to place an ad in your local paper. Choose one small ad to run for say 4 issues, since this is usually more effective than one large ad run for a single issue and should also get you a discount on the price for a multiple edition run. I find that a website now generates around 80%+ of my new bookings. if you start up and want some help in building a website then let me know and I'll try and help. Tom is also good at website building as well
Also for advertising - have some business cards done and pin these on noticeboards in leisure centres, Schools, Church Halls etc. You can find more info on advertising if you look around this forum.
If you need anymore information then please post here, or email me chris@dj-supplies.co.uk
Chris